Related posts and read next

'use client';

import { useRef, useState, useEffect } from 'react';
import { cn, useTexts } from '@/lib/kit';
import { Icon, type IconName } from '@/components/ui/icon';
import { Eyebrow, Section } from '@/components/ui/section';
import { Reveal } from '@/components/ui/reveal';
import { Stagger } from '@/components/ui/motion';

/*
 * What to read, watch or open next, at the end of an article or page.
 * Items can be of different kinds (article, guide, video, page, download,
 * podcast), each with its own icon and label.
 *
 *   cards     three cards with picture, kind and time, a sideways row on phones and tablets
 *   list      a compact numbered list in two columns, for the end of a text
 *   featured  one large pick beside a short list with small pictures
 *   next-prev the previous and next piece as two large links, more below
 */

export type RelatedContentVariant = 'cards' | 'list' | 'featured' | 'next-prev';
export type RelatedKind = 'article' | 'guide' | 'video' | 'page' | 'download' | 'podcast';

export interface RelatedItem {
  title: string;
  href: string;
  kind?: RelatedKind;
  excerpt?: string;
  /** As shown, e.g. "6 min read", "12:40" or "PDF, 2 MB" */
  meta?: string;
  /** A picture, e.g. <img … /> */
  media?: React.ReactNode;
}

const TEXTS = {
  en: { article: 'Article', guide: 'Guide', video: 'Video', page: 'Page', download: 'Download', podcast: 'Podcast', all: 'See all', previous: 'Previous', next: 'Next', more: 'More on this topic', scroll: 'Related content, scroll sideways', back: 'Show previous', forward: 'Show next' },
  de: { article: 'Artikel', guide: 'Ratgeber', video: 'Video', page: 'Seite', download: 'Download', podcast: 'Podcast', all: 'Alle ansehen', previous: 'Vorheriger Beitrag', next: 'Nächster Beitrag', more: 'Mehr zum Thema', scroll: 'Weiterlesen, seitlich scrollen', back: 'Vorherige zeigen', forward: 'Nächste zeigen' },
};
type Texts = (typeof TEXTS)['en'];

const KIND_ICON: Record<RelatedKind, IconName> = { article: 'newspaper', guide: 'book-open', video: 'play-circle', page: 'file', download: 'download', podcast: 'headphones' };

export interface RelatedContentProps {
  variant?: RelatedContentVariant;
  eyebrow?: React.ReactNode;
  title?: React.ReactNode;
  description?: React.ReactNode;
  items: RelatedItem[];
  /** A link to everything, beside the title */
  allHref?: string;
  /** Heading level of the item titles follows the section title */
  labels?: Partial<Texts>;
  className?: string;
}

const focus = 'outline-none focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-solid focus-visible:outline-ring';

function Kind({ kind = 'article', t, className }: { kind?: RelatedKind; t: Texts; className?: string }) {
  return (
    <span className={cn('inline-flex items-center gap-1.5 text-[12px] font-medium text-[color-mix(in_oklab,var(--primary)_75%,var(--muted-foreground))]', className)}>
      <Icon name={KIND_ICON[kind]} size={14} />
      {t[kind]}
    </span>
  );
}

function Picture({ media, className }: { media?: React.ReactNode; className?: string }) {
  return (
    <span data-clip-ok className={cn('relative block overflow-hidden bg-muted', className)}>
      <span className="absolute inset-0 block transition-transform duration-700 ease-[var(--ease-kit)] group-hover:scale-[1.04] motion-reduce:transition-none [&>*]:size-full">{media}</span>
    </span>
  );
}

function Head({ p, t }: { p: RelatedContentProps; t: Texts }) {
  if (!p.title && !p.eyebrow && !p.allHref) return null;
  return (
    <div className="mb-10 flex flex-col gap-5 sm:mb-12 sm:flex-row sm:items-end sm:justify-between">
      <div className="max-w-[40rem]">
        {p.eyebrow && <Eyebrow>{p.eyebrow}</Eyebrow>}
        {p.title && <h2 className="text-balance text-h2 font-semibold text-foreground">{p.title}</h2>}
        {p.description && <p className="mt-4 text-pretty text-lead text-muted-foreground">{p.description}</p>}
      </div>
      {p.allHref && (
        <a href={p.allHref} className={cn('group inline-flex min-h-11 shrink-0 items-center gap-1.5 self-start rounded-md text-[14px] font-medium text-foreground sm:self-auto', focus)}>
          {t.all}
          <Icon name="arrow-right" size={15} className="transition-transform duration-300 group-hover:translate-x-0.5" />
        </a>
      )}
    </div>
  );
}

/* ------------------------------------------------------------------ */

function Cards({ p, t }: { p: RelatedContentProps; t: Texts }) {
  const row = useRef<HTMLUListElement>(null);
  const [edge, setEdge] = useState<'start' | 'middle' | 'end'>('start');
  useEffect(() => {
    const el = row.current;
    if (!el) return;
    const update = () => {
      const max = el.scrollWidth - el.clientWidth;
      setEdge(el.scrollLeft < 8 ? 'start' : el.scrollLeft > max - 8 ? 'end' : 'middle');
    };
    update();
    el.addEventListener('scroll', update, { passive: true });
    return () => el.removeEventListener('scroll', update);
  }, []);
  const step = (dir: 1 | -1) => {
    const el = row.current;
    if (el) el.scrollBy({ left: dir * el.clientWidth * 0.8, behavior: 'smooth' });
  };
  return (
    <>
      <Head p={p} t={t} />
      <ul
        ref={row}
        tabIndex={0}
        aria-label={t.scroll}
        className={cn(
          'kit-no-scrollbar -mx-6 flex snap-x snap-mandatory scroll-px-6 gap-4 overflow-x-auto px-6 pb-2 outline-none focus-visible:outline-2 focus-visible:outline-solid focus-visible:outline-ring sm:gap-5 lg:mx-0 lg:grid lg:grid-cols-3 lg:overflow-visible lg:px-0 lg:pb-0',
          edge === 'start' ? 'max-lg:kit-fade-end' : edge === 'end' ? 'max-lg:kit-fade-start' : 'max-lg:kit-fade-x',
        )}
      >
        {p.items.map((it, i) => (
          <Reveal as="li" key={it.href + i} delay={i * 80} className="w-[82%] shrink-0 snap-start sm:w-[44%] lg:w-auto">
            <a href={it.href} className={cn('group flex h-full flex-col overflow-hidden rounded-xl border border-border bg-card shadow-[var(--highlight),var(--shadow-sm)] transition-[transform,box-shadow] duration-300 ease-[var(--ease-kit)] hover:-translate-y-1 hover:shadow-[var(--highlight),var(--shadow-md)] motion-reduce:hover:translate-y-0', focus)}>
              <Picture media={it.media} className="aspect-[16/10] border-b border-border" />
              <div className="flex flex-1 flex-col p-5">
                <Kind kind={it.kind} t={t} />
                <h3 className="mt-3 text-balance text-[17px] font-semibold leading-snug tracking-[-0.015em] text-foreground">{it.title}</h3>
                {it.excerpt && <span className="mt-2 line-clamp-3 text-pretty text-[14.5px] leading-relaxed text-muted-foreground">{it.excerpt}</span>}
                <span className="mt-auto flex items-center justify-between gap-3 pt-5 text-[13px] text-muted-foreground">
                  <span>{it.meta}</span>
                  <Icon name="arrow-up-right" size={16} className="text-foreground transition-transform duration-300 group-hover:-translate-y-0.5 group-hover:translate-x-0.5" />
                </span>
              </div>
            </a>
          </Reveal>
        ))}
      </ul>
      {p.items.length > 1 && (
        <div className="mt-4 flex justify-end gap-2 lg:hidden">
          <button type="button" aria-label={t.back} disabled={edge === 'start'} onClick={() => step(-1)} className={cn('flex size-11 cursor-pointer items-center justify-center rounded-full border border-border bg-background text-foreground transition-opacity disabled:cursor-default disabled:opacity-40', focus)}>
            <Icon name="arrow-left" size={16} />
          </button>
          <button type="button" aria-label={t.forward} disabled={edge === 'end'} onClick={() => step(1)} className={cn('flex size-11 cursor-pointer items-center justify-center rounded-full border border-border bg-background text-foreground transition-opacity disabled:cursor-default disabled:opacity-40', focus)}>
            <Icon name="arrow-right" size={16} />
          </button>
        </div>
      )}
    </>
  );
}

function List({ p, t }: { p: RelatedContentProps; t: Texts }) {
  return (
    <div className="mx-auto max-w-[60rem]">
      <Head p={p} t={t} />
      <Stagger as="ol" step={60} className="grid grid-cols-[minmax(0,1fr)] border-t border-border md:grid-cols-2 md:gap-x-10">
        {p.items.map((it, i) => (
          <li key={it.href + i} className="border-b border-border">
            <a href={it.href} className={cn('group grid min-h-11 grid-cols-[2rem_minmax(0,1fr)_auto] items-start gap-3 rounded-md py-5', focus)}>
              <span className="pt-0.5 text-[13px] font-medium tabular-nums text-subtle-foreground transition-colors group-hover:text-primary">{String(i + 1).padStart(2, '0')}</span>
              <div className="min-w-0">
                <h3 className="text-pretty text-[16px] font-semibold leading-snug text-foreground decoration-border-strong underline-offset-4 group-hover:underline">{it.title}</h3>
                <span className="mt-1.5 flex flex-wrap items-center gap-x-3 gap-y-1">
                  <Kind kind={it.kind} t={t} />
                  {it.meta && <span className="text-[12.5px] text-muted-foreground">{it.meta}</span>}
                </span>
              </div>
              <Icon name="arrow-right" size={16} className="mt-1 text-muted-foreground transition-[transform,color] duration-300 group-hover:translate-x-1 group-hover:text-foreground" />
            </a>
          </li>
        ))}
      </Stagger>
    </div>
  );
}

function Featured({ p, t }: { p: RelatedContentProps; t: Texts }) {
  const [first, ...rest] = p.items;
  if (!first) return null;
  return (
    <>
      <Head p={p} t={t} />
      <div className="grid grid-cols-[minmax(0,1fr)] gap-6 lg:grid-cols-[minmax(0,7fr)_minmax(0,5fr)] lg:gap-10">
        <Reveal effect="scale">
          <a href={first.href} className={cn('group relative flex h-full min-h-[22rem] flex-col justify-end overflow-hidden rounded-2xl border border-border bg-muted shadow-[var(--shadow-md)] sm:min-h-[26rem]', focus)}>
            <Picture media={first.media} className="!absolute inset-0" />
            <span aria-hidden className="absolute inset-0 bg-[linear-gradient(to_top,rgb(0_0_0/0.88),rgb(0_0_0/0.62)_45%,rgb(0_0_0/0.1)_85%)]" />
            <div className="dark relative p-6 sm:p-8">
              <Kind kind={first.kind} t={t} className="text-white/85" />
              <h3 className="mt-3 max-w-[30rem] text-balance text-[clamp(1.375rem,1.1rem+1vw,1.875rem)] font-semibold leading-tight tracking-[-0.025em] text-white">{first.title}</h3>
              {first.excerpt && <span className="mt-3 block max-w-[32rem] text-pretty text-[15px] leading-relaxed text-white/80">{first.excerpt}</span>}
              <span className="mt-5 inline-flex items-center gap-2 text-[14px] font-medium text-white">
                {first.meta}
                <Icon name="arrow-right" size={15} className="transition-transform duration-300 group-hover:translate-x-1" />
              </span>
            </div>
          </a>
        </Reveal>
        <Stagger as="ul" step={90} className="flex flex-col divide-y divide-border">
          {rest.map((it, i) => (
            <li key={it.href + i} className="first:pt-0 [&:not(:first-child)]:pt-4 [&:not(:last-child)]:pb-4 lg:flex lg:flex-1 lg:items-center">
              <a href={it.href} className={cn('group grid w-full grid-cols-[6.5rem_minmax(0,1fr)] items-center gap-4 rounded-lg sm:grid-cols-[8rem_minmax(0,1fr)]', focus)}>
                <Picture media={it.media} className="aspect-[4/3] rounded-lg border border-border" />
                <div className="min-w-0">
                  <Kind kind={it.kind} t={t} />
                  <h3 className="mt-1.5 text-pretty text-[15.5px] font-semibold leading-snug text-foreground decoration-border-strong underline-offset-4 group-hover:underline">{it.title}</h3>
                  {it.meta && <span className="mt-1 block text-[12.5px] text-muted-foreground">{it.meta}</span>}
                </div>
              </a>
            </li>
          ))}
        </Stagger>
      </div>
    </>
  );
}

function NextPrev({ p, t }: { p: RelatedContentProps; t: Texts }) {
  const [prev, next, ...more] = p.items;
  const pager = (it: RelatedItem | undefined, dir: 'prev' | 'next') => {
    if (!it) return <span className="hidden sm:block" />;
    const isNext = dir === 'next';
    return (
      <a
        href={it.href}
        rel={isNext ? 'next' : 'prev'}
        className={cn(
          'group relative flex min-h-36 flex-col justify-between gap-6 overflow-hidden rounded-2xl border border-border bg-card p-6 shadow-[var(--highlight),var(--shadow-sm)] transition-[border-color,box-shadow] duration-300 hover:border-border-strong hover:shadow-[var(--highlight),var(--shadow-md)] sm:p-7',
          isNext && 'sm:text-right',
          focus,
        )}
      >
        <span aria-hidden className={cn('pointer-events-none absolute inset-y-0 w-1/2 opacity-0 transition-opacity duration-500 group-hover:opacity-100', isNext ? 'right-0 bg-[radial-gradient(closest-side_at_100%_50%,var(--glow),transparent)]' : 'left-0 bg-[radial-gradient(closest-side_at_0%_50%,var(--glow),transparent)]')} />
        <span className={cn('relative flex items-center gap-2 text-[13px] font-medium text-muted-foreground', isNext && 'sm:justify-end')}>
          {!isNext && <Icon name="arrow-left" size={16} className="transition-transform duration-300 group-hover:-translate-x-1" />}
          {isNext ? t.next : t.previous}
          {isNext && <Icon name="arrow-right" size={16} className="transition-transform duration-300 group-hover:translate-x-1" />}
        </span>
        <div className="relative">
          <h3 className="text-balance text-[clamp(1.125rem,1rem+0.6vw,1.375rem)] font-semibold leading-snug tracking-[-0.02em] text-foreground">{it.title}</h3>
          <span className={cn('mt-2 flex items-center gap-3 text-[13px] text-muted-foreground', isNext && 'sm:justify-end')}>
            <Kind kind={it.kind} t={t} />
            {it.meta && <span>{it.meta}</span>}
          </span>
        </div>
      </a>
    );
  };
  return (
    <nav aria-label={typeof p.title === 'string' ? p.title : t.more} className="mx-auto max-w-[60rem]">
      <Head p={p} t={t} />
      <Reveal className="grid grid-cols-[minmax(0,1fr)] gap-4 sm:grid-cols-2 sm:gap-5">
        {pager(prev, 'prev')}
        {pager(next, 'next')}
      </Reveal>
      {more.length > 0 && (
        <Reveal delay={150} className="mt-10 border-t border-border pt-6">
          <p className="text-[13px] font-medium text-subtle-foreground">{t.more}</p>
          <ul className="mt-2 flex flex-col sm:flex-row sm:flex-wrap sm:gap-x-8">
            {more.map((it, i) => (
              <li key={it.href + i}>
                <a href={it.href} className={cn('group inline-flex min-h-11 items-center gap-2 rounded-md text-[14.5px] text-foreground', focus)}>
                  <Icon name={KIND_ICON[it.kind ?? 'article']} size={15} className="text-muted-foreground" />
                  <span className="underline decoration-border-strong underline-offset-4 transition-colors group-hover:decoration-foreground">{it.title}</span>
                </a>
              </li>
            ))}
          </ul>
        </Reveal>
      )}
    </nav>
  );
}

/**
 * Related content for the end of a page: cards, a numbered list, one large
 * pick with a short list, or previous and next with more below.
 *   <RelatedContent variant="cards" title="Read next" items={[{ title, href, kind: 'guide', meta: '6 min', media }]} />
 */
export function RelatedContent(props: RelatedContentProps) {
  const { variant = 'cards', className, labels } = props;
  const t = useTexts(TEXTS, labels);
  return (
    <Section spacing="sm" className={cn('border-t border-border', className)}>
      {variant === 'list' ? <List p={props} t={t} /> : variant === 'featured' ? <Featured p={props} t={t} /> : variant === 'next-prev' ? <NextPrev p={props} t={t} /> : <Cards p={props} t={t} />}
    </Section>
  );
}